Process for the manufacture of lower aliphatic esters



L. ALHERITIERE ETAL April 2, 1957 United States Patent() PROCESS FOR THE MANUFACTURE F LOWER ALIPHATIC ESTERS Louis Alheritiere and Jules Mercier, Melle, Deux-Sevres,

France, assiguors to Les Usines de Melle (Societe AnolFryme), Saint-Leger-les Melle, France, a corporation of rance Application January 5, 1955, Serial No. 479,979

Claims priority, application France February 18, 1954 4 Claims. (Cl. 2450-488) The invention relates to the process for the manufacture of lower aliphatic esters. Y

A conventional process of manufacture of such lower esters consists in continuously introducing the acid to be esterified and an amount of alcohol in excess of -40% over the theoretical proportion, into a reaction vessel containing an esterication catalyst such as sulphuric acid, and continuously distilling the reaction products in a distilling column surmounting the esterification vessel. The ester and kwater resulting from the esterication reaction are withdrawn from the head of the column together with the excess alcohol, and the vapors of acid are prevented from rising to the top by reiiuxing part of the distillate.

An object of the present invention is to provide a simple, efficient process for the manufacture of such esters which will increase the productive capacity of a given esterification apparatus employing the conventional process mentioned, While reducing the heat expense as compared therewith.

The invention accordingly consists of the novel processes and steps of processes, specific embodiments of which are described hereinafter by way of example and in accordance with which we now prefer to practice the invention.

We have found, in accordance with our invention, that such process may be carried out by continuously introducing acid and alcohol to be esteriiied into a catalytic esterification bath containing at least 20% by weight of an auxiliary liquid which has a boiling temperature of at least 120 C., such boiling temperature being above that of the ester to be produced. Theauxiliary liquid is one which is stable under the esterification conditions. It is miscible with the other constituents of the bath and does not cause displacement of water therefrom. Such auxiliary liquid does not provide, with any of the other constituents of the bath, any azeotropic mixture which has a lower boiling point than that of the azeotropic mixture of Water with the ester produced. The bath is maintained at the boiling. Continuous esterifcation occurs. The ester is continuously recovered by distillation. During the process the auxiliary liquid remains behind and is not distilled from the body of the liquid where the esteriiication is occurring.

The auxiliary liquid is an organic compound or mixture of organic compounds taken from various classes, more particularly esters, ethers, ketones and hydrocarb ons. As esters constituting such auxiliary liquid there are preferably used those derived from the saine acid as that to be esteried and from an alcohol having a boiling point above that of the alcohol to be esteriiied. For instance, but without limitation, we may use butyl acetate, beta ethoxy ethyl acetate and amyl acetate. As ethers there may be used, for example, butyl oxides. As ketones, for example, a dipropyl ketone may be employed. `As hydrocarbons, for example, one may use xylene.

The auxiliary liquid in the bath results in an increased boiling temperature, favoring removal by distillation ot 2,787,636 Patented Apr. 2, 1957 "ice the reaction water. The so-lowered water content of the bath and the increased temperature result in increased reaction speed, allowing the excess amount of alcohol used to be considerably reduced, thus facilitating separation of water by decantation of the distillate withdrawn from the head of the column. It is known that lower aliphatic alcohols, which are soluble in water in any proportions, increase the mutual solubility of water and esters. By our process, using less alcohol than heretofore, separation of water is more readily effected. These new results are important in the economical operation of the process.

This invention applies more particularly to the manufacture of esters having no more than 6 carbon atoms in the molecule, from aliphatic acids and alcohols having no more than 4 carbon atoms. The invention is especially suitable, though not restricted, to making esters of lower aliphatic alcohols, which alcohols are soluble in water in all proportions, such as methyl, ethyl, isopropyl and allyl alcohols. It is also applicable to other 4-carbon alcohols of lesser solubility in water.

The accompanying drawing forming part of this application is a ow sheet showing a preferred method of carrying out the invention.

The following are examples of the process as we now prefer to practice it. It is to be understood that the examples are illustrative and that the invention is not to be considered as restricted thereto except as indicated in the appended claims.

Units shown in the flow sheet are referred to in the examples.

Example 1.--Manufactare of ethyl acetate An esterifcation vessel 4 is charged initially with butyl acetate as an auxiliary liquid, and sulphuric acid as an esterification catalyst.

The vessel in normal run contains 1200 kg. of reaction bath, the composition of which will be indicated herebelow. This vessel is continuously fed with 256 kg. per hour of acetic acid from tank 2 and 263 kg. of ethyl alcohol from tank 3.which receives, on the one hand, pure ethyl alcoholof vol. percent strength from tank 1, and, on the other hand, recovered alcohol containing ethyl acetate, from column 22, as explained herebelow. Constant liquid level isr maintained in tank 3 by means of a float-valve which automatically allows fresh alcohol to ow from tank 2.

Vessel 4 is heated by means of a coil 5 in such a manner that 330,000 calories are absorbed per hour by condenser 7 connected with distilling column 6 which is disposed above vessel 4.

The condensate from condenser 7 is mixed with water in a mixer 8 which preferably is a little tower filled with Raschig rings. The added Water extracts the alcohol from the condensate. The mixture is introduced into a decanter 9 where it separates into two layers. The upper layer contains less water than does the distillate as withdrawn from column 6, and this feature permits removal of the distilled reaction water and Water initially contained in the starting alcohol; For this purpose the upper layer is drawn ofi through pipe 10' at a suitable rate. Part thereof is refluxed through pipe 11 to the top of column 6. The remainder, amounting to 420 kg. per hour, is sent through pipe 12 to a washing tower 13, preferably illed with Raschig rings, which is fed with water through pipev 1 at a rate of 300 liters per hour.

The washing with water in tower 13 entirely removes the small amount of alcohol still contained in the raw ester constituting the upper layer from decanter 9. The water issuing'from tower 13, which is .saturated with ethyl acetate and contains a little alcohol, is recycled by `pump to mixer .8 to be mixed .with the `distillate from column 6 as described above.

From the top part of tower 13 there is withdrawn, through pipe 1&6, 387 kg. .per hour of `waterfsaturated ethyl acetate, which :then ris dehydrated lby distillation .in a little distilling column 17 from the base .of which there is obtained, through pipe 18, 375 kg. per hour of anhydrous ethyl acetate. The distillate 'from icolumn 17 is `condensed `in condenser 19 and .allowed 'to settle in decanter 20. The lower layer from `decanter 2), amounting to l2 kg. per hour, is fed through pipe 21 to a recovery column 22, while the upper `layer is reuxed through .pipe 23 tothe top .of column 17.

The lower layer from decanter 9 is fed to .column 22 together with that from decanter 20. The condensate from condenser 2.4 connected with :column 22 contains, by weight, 18% of alcohol, 74% of ethyl acetate and 8% of water, Part of this .condensate is reuxed to the top of 4column 22 through pipe 25. The remainder, amounting `to 50kg. Aper jhour, is recycled through .valved pipe 2,6 to tank 3 which receives 213 kg. per hour .of fresh, 95 vol. percentalcohol, i. e. 197 kg. per hour of purealcohol, from -tank 2 which are automatically admitted by the oat-valve.

Thus, vessel 4 is `fed with a ,total amount `of 206 kg. per hour ,of pure alcohol, this representing .an excess .of 9 kg. over the theoretical amountrequired toesterify .the 2,56 kg. of acetic acid fed per hour, the .excess proportion of alcohol thus being 4.5% only.

ln normal run, the weight composition of the esteritication bath in vessel 4 is substantially as follows:

Percent Butyl acetate 6l Butyl alcohol 0.3 Ethyl acetate 10.2 Acetic acid 25 Water 1.5 Ethyl alcohol e 0.8 Sulphuric acid 1.2

The boiling temperature of this bath is 110 C.

The steam expense -or expenditure per kg. of ester produced is of 1.7 kg. in vessel `4 and 0.4 kg. in column 22, i. e. a total amount of 2.1 kg.

For sake of comparison, a similar operation but carried out without auxiliary liquid gives the following results:

Temperature of the bath-92 C. (insteadof 110 C..).

Ester produced-210 kg. per hour (instead of 375 kg).

Excess alcohol to be used in vessel 4--l5% .(instead Amount of wash water to be used in tower 13-500 liters per hour, i. e. 2.4 liters per kg. of ester produced (instead of 0.8 liter).

Steam expense per kg. of ester produced-3.1 kg. in vessel 4 and 1 kg. in column 22, i. e. a total amount of 4.1 kg. (instead of 2.1 kg.).

Example 2.-Marzufact1lre of |isopropyl acetate The apparatus and process are the same as in Example l except for changes in operating conditions as indicated below.

The auxiliary liquid ,is beta-ethoxy-ethyl acetate, employed in such a quantity that the esterification bath contains by weight thereof. The temperature of the bath is maintained at 110 C.

The operating `conditions are as follows:

Weight of material in bath-1200 kg.

Acetic acid feed (from tank 1)-236 kg. -per hour.

Fresh isopropyl alcohol feed (from tank 2)-272 kg. per hour of water-isopropyl alcohol azeotropic mixture containing 87% by weight of isopropyl alcohol.

Total alcoholic feed to vessel 4 (from tank 3)-331 kg.

per hour.

Percent Beta-ethoxy-ethyl acetate 50 Ethoxy ethylene glycol 0.5 lsopropyl. acetate 16 Acetic acid 30 Water 1.5 isopropyl alcohol 1 Sulfnric acid l xFor sake of comparison, the production by a similar process carried out in the same apparatus but without auxiliary liquid amounts to only 250 kg. per hour of ester. The temperature of the bath is 92 C. An excess of alcohol ot 40% isused and 800 liters per hour of wash water are employed. The steam expense .per kg. of ester amounts to 2 kg. in vessel 4 and 0.6 kg. in column 22, i. e. a total amount of 2.6 kg.

Example 3.Manufactm'e of propyl formate The apparatus and process are the same as in the preceding examples except for certain changes in the operating conditions as given below.

The auxiliary liquid is n-butyl oxide, employed -in such aquantity that the bath contains 70% "by weight thereof. The bath is so heated that its operating temperature is C.

The operating conditions are as follows:

Volume of the bath in vessel 4--1500 liters.

Formic acid content in the bath- 10%.

Anhydrous forrnic acid feed (from tank 1).230 kg. per

hour.

Anhydrous fresh propyl alcohol feed (from tank 2)- 300 kg. per hour.

Total alcoholic feed to vessel 4 (from tank 3).-330 kg.

per hour.

Excess alcohol fed-5%.

Wash water-200 liters per hour.

Weight composition of bath: Percent Butyl oxide 70 Propyl formate 9 Formia acid 14 Water 1.5 Propyl alcohol 4.3 Sulfuric acid 12 Production of anhydrous propyl formate-438 kg. per

hour.

Steam `expense-1.6 kg. in vessel 4 and 0.5 kg. in column 22, i. e. a total amount of 2.1 kg.

The number of calories absorbed were-280,000.

Example 4.-Ma1mff!cture of isopropyl pmpionatc The apparatus and process are the same as in the preceding examples except for certain changes in the operating conditions as given below.

The auxiliary liquid is di-n-propyl ketone constituting 35% 'by weight of the bath. rIlhe bath is maintained at ya temperature of C.

The operating conditions are as follows:

Volume of the bath in vessel 4`1200 liters. Anhydrous propionic acid feed (from tank `1)--345 kg.

per hour. Fresh isopropyl alcohol feed (from tank 2)--362 kg.

*ananas Percent Di-n-propyl ketone 35 Isopropyl propionate 32 Propionic acid 30.4 Water 0.8 Isopropyl alcohol 0.8 Sulfuric acid 1 Production of anhydrous isopropyl propionate-600 kg.

per hour.

i Steam expense-1.9 kg. in vessel 4 and 0.3 kg. in column 22, i. e. a total amount of 2.2 kg. Calories absorbed-570,000.

Example 5.-Manufacture of ethyl acetate The process of Example l was repeated with substantially the same results by using a mixture of equal parts by weight of butyl acetate and beta ethoxy ethyl acetate, instead of using butyl acetate alone.

The operating conditions and data were the same as in Example 1, except that the bathv content was as follows:

Percent Butyl acetate- 3() Beta ethoxy ethyl acetate 30 Butyl alcohol 0.1 Ethoxy ethylene glyco 0.2 Ethyl acetate 10,5 Acetic avid 26 Water 1.2 Ethyl alcohol 8 Sulfuric acid 1.2

The production and steam expense figures were as in Example 1.

What we claim is:

1. A process for producing lower aliphatic esters containing 3 to 6 carbon atoms, which comprises continuously introducing an alkanoic acid and -alcohol selected from the group consisting of an alkanol and an alltenol each containing from 1 to 4 carbon atoms into a boiling catalytic esterication bath, said alcohol being introduced in a quantity less than 20% excess of the theoretical amount required for producing the ester from said acid, said bath containing at least 20% by Weight of an auxiliary liquid which has a boiling temperature of at least 120 C. and above that of the ester to be produced, is stable under the esterication conditions, is miscible with the other constituents of the bath, does not cause displacement of water therefrom and does not give with the constituents of the bath any aieotropic mixture of lower boiling point than that of the azeotropic mixture of water with the said ester, and continuously distilling the ester formed.

2. A process for producing lower aliphatic esters con taining 3 to 6 carbon atoms, which comprises continuously introducing an alkanoic acid and alcohol selected from the group consisting of an alkanol and an alkenol each containing from 1 to 4 carbon atoms into a boiling catalytic esteriication bath, said alcohol being introduced in a quantity less than 20% excess of the theoretical amount required for producing the ester from said acid, said bath containing at least 20% by vweight of an auxiliary liquid ester derived from the same acid as that to be esteriled and from an alcohol having a boiling point above that of the alcohol to be esterilied, said auxiliary ester having a yboiling temperature of at least C. and above that of the ester to be produced, being stable under the esterication conditions and miscible with the other constituents of the bath, not causing displacement of water therefrom and not giving with the constituents of the bath any azeotropic mixture of lower boiling point than that of the azeotropic mixture of water with the ester produced, and continuously distilling the ester formed.

3. A process for producing lower aliphatic esters containing 3 to 6 carbon atoms, which comprises continuously introducing an alkanoic acid land alcohol selected from the group consisting of an an alkanol and an alkenol each containing from 1 to 4 carbon atoms into a boiling catalytic esterication bath, said alcohol being introduced in a quantity less than 20% excess of the theoretical amount required for producing the ester from said acid, said bath containing at least 20% by weight of a butyl oxide and continuously distilling the ester formed.

4. A process for producing lower aliphatic esters containing 3 to 6 carbon atoms, which comprises continuouslyr introducing an alkanoic acid and alcohol selected from the group consisting of an alkanol land an alkenol each containing from 1 to 4 carbon atoms into a boiling catalytic esteritication bath, said alcohol being introduced in a quantity less than 20% excess of the theoretical amount required for producing the ester from said acid, said bath containing at least 20% by weight of a dipropyl ketone amd continuously distilling the ester formed.

References Cited in the le of this patent UNITED STATES PATENTS 2,575,722 OTHER REFERENCES Groggins: Unit Processes in Organic Synthesis (1952), pp. 612-615. 

1. A PROCESS FOR PRODUCING LOWER ALIPHATIC ESTERS CONTAINING 3 TO 6 CARBON ATOMS, WHICH COMPRISES CONTINUOUSLY INTRODUCING AN ALKANOIC ACID AND ALCOHOL SELECTED FROM THE GROUP CONSISTING OF AN ALKANOL AND AN ALKENOL EACH CONTAINING FROM 1 TO 4 CARBON ATOMS INTO A BOILING CARALYTIC ESTERIFICATION BATH, SAID ALCOHOL BEING INTRODUCED IN A QUANTITY LESS THAN 2/% EXCESS OF THE THEORETICAL AMOUNT REQUIRED FOR PRODUCING THE ESTER FROM SAID ACID, SAID BATH CONTAINING AT LEAST 20% BY WEIGTH OF AN AUXILIARY LIQUID WHICH HAS A BOILING TEMPERATURE OF AT LEAST 120* C. AND ABOVE THAT OF THE ESSTER TO BE PRODUCED, IS STABLE UNDER THE ESTERIFICATION CONDITIONS, IS MISCIBLE WITH THE OTHER CONSTITUENTS OF THE BATH, DOES NOT CAUSE DISPLACEMENT OF WATER THEREFROM AND DOES NOT GIVE WITH THE CONSTITUENTS OF THE BATH ANY AZEOTROPIC MIXTURE OF LOWER BOILING POINT THAN THAT OF THE AZEOTROPIC MIXTURE OF WATER WITH THE SAID ESTER, AND CONTINUOUSLY DISTILLING THE ESTER FORMED. 